You have rigth now a " big " true problem with your Sonata speakers. Yes I know that you like it but this " you like it " just does not helps to disappears the problem.
Problem name is IMD ( InterModulationDistortion. ) high levels ( that you are accustom to. ) and THD too and the problem comes because the manufacturer designer choosed as crossover frequency 1.5khz and this means that that driver/woofer handled frequencies as low as 25hz all the way over 1.5khz.
We don’t add a paiir of self powered true subwoofers to achieve lower bass levels, this is an advantage to integrates subs but the main issue is to lower the IMD/THD of your room/system and this always will has a rewards because you will listening better quality performance levels with a lot lower distortion levels.
Here you can read the why of my take about:
https://forum.audiogon.com/discussions/do-you-think-you-need-a-subwoofer/post?postid=310058#310058
You can do it with your today Sonatas crossing two a pair of TRUE self powered subwoofers that today normally comes with an integrated software and microphone to make the rigth system integration.
Or you can do it two with these excellent monitors:
http://www.silverlineaudio.com/main/index.php?option=com_content&view=article&id=46&Item...
That’s why I posted to the gentleman that asked for the Wilson Alexx V one alternative with monitors/subs that with any single doubt will outperforms any full range passive speakers.
Unfortunatelly the overall knowledge levels on the specific issue is lower than what we think and not even " professionals " reviewers as M.fremer has it when for years is using full range Wilson speakers. Yes he is wrong when does it and the overall full range speaker owners could achieve good rewards if just think/learn how to outperforms what they have rigth know with a really small investment on monitors/subs alternative. That gentleman on the Wilson V instead to ask for a better alternative just wants to follows behind what he is accustom too even if it’s not the best path for him.
High Quality room/system levels is not about just money but mainly about knowledge levels.
Regards and enjoy the MUSIC NOT DISTORTIONS,
R.